Teen Eye Chart Screening Misses Some Problems

Action Points

Note that the standard school-based vision screening for adolescents includes a test of visual acuity but not dilated refraction error.

Explain to interested parents that the standard visual acuity screening at school may not be reliable for detection of farsightedness.

Traditional school-based vision screening tests with an eye chart can accurately detect nearsightedness but not other types of refractive errors in adolescents, researchers found.

Among a large cohort of 12-year-olds, the ability to read at least 45 letters on the eye chart (6/9.5 visual acuity) detected myopia with sensitivity of 97.8% and specificity of 97.1%, according to Jody Fay Leone, BAppSci (Orth), of the University of Sydney Cumberland Campus in Lidcombe, Australia, and colleagues.

However, no cutoff could reliably indicate clinically significant farsightedness or astigmatism, they reported in the July issue of the Archives of Ophthalmology.

Age 12 is when nearsightedness typically begins to appear in children, but astigmatism and farsightedness occur far less often at this age, noted David G. Hunter, MD, of Children's Hospital Boston and Harvard and a clinical correspondent for the American Academy of Ophthalmology.

"The main reason for screening in that age is to make sure that their vision is not interfering in any way with their ability to perform at their top level in school," he said in an interview with MedPage Today. "It's reassuring to know that the standard visual acuity test done in school is going to identify those kids [with myopia] and get them into treatment so they can see the board."

Poorer performance for eye charts in detecting astigmatism likely isn't that critical since clinically significant cases would get picked up as poor vision and referred to an ophthalmologist, Hunter added.

However, that visual acuity screening appeared unreliable for detecting farsightedness is a bigger concern, Hunter noted.

Despite testing normal for vision screening at school, "if a child is 12 years old and struggling at school and nobody can understand why, it's going to be in everyone's interest to have his eyes tested by a professional," he said.

Leone's group analyzed the Sydney Myopia Study, a substudy of the school-based, cross-sectional Sydney Childhood Eye Survey that attempted to screen refraction and eye health of all children in two age cohorts at 21 randomly selected secondary schools in Sydney.

The analysis included 4,497 observations with data pooled for both eyes of students in their seventh year of school (mean age 12.7 years).

The average visual acuity was 54 letters (6/6+1).

Refraction testing indicated significant myopia of -1.00 D or less in 6.4% of the children, significant hyperopia of +2.00 D or more in 5.4%, and significant astigmatism of -1.00 D or less in 4.1%.

The researchers called the correlation with visual acuity complex.

Altogether, visual acuity detected any significant refractive error with sensitivity of 72.2% and specificity of 93.3 using the best cutoff of 53 letters (6/6-2).

Accuracy for hyperopia alone was poor at even the best cutoff of 57 letters of visual acuity (6/6+2) with sensitivity of 69.2% and specificity of 58.1%.

For clinically significant astigmatism, the best visual acuity cutoff of 55 letters (6/6) likewise was low with sensitivity of 77.4% and specificity of 75.4%.

Since these cutoffs equated to essentially normal vision, the test would be "quite meaningless" for hyperopia and astigmatism and lead to "unacceptably high" levels of unnecessary referral for further vision testing, the researchers wrote in the paper.

Missing clinically significant hyperopia can have significant implications for these children based on prior research showing lower educational attainment and less reading among them, Leone's group added.

"This implies that accommodative effort may be maintained for the brief duration of visual acuity testing but cannot be sustained for longer-term tasks such as reading books," they wrote in the Archives.

One strategy that deserves further validation may be to use a +4.00 lens as a fogging technique that would keep these kids from overcoming their refractive error by accommodation, they suggested.

"Further research on detecting these forms of refractive error more reliably during screening is required," they concluded in the paper.

The study was supported by a grant from the National Health and Medical Research Council of Australia and the Vision Co-operative Research Centre, by a grant from the Australian Research Council, and by a National Health and Medical Research Council Biomedical postgraduate research scholarship.

The researchers reported that they had no financial conflicts of interest to disclose.

Hunter reported being founder of Rebiscan, a company developing a device for vision screening in preschool-age children.

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